It is common practice to run, land, set and retrieve downhole tools within the borehole of a well to perform various functions including sealing the bore of the well or for carrying a measuring device for monitoring parameters such as pressure or temperature within the well. Typically the borehole of a well is cased using drillpipe, casing or tubing string which is designed in such as way as to provide predetermined locations for landing and setting such downhole tools.
Conventionally, downhole tools are landed and set at specific predetermined locations by relying on the interaction between the tool and a restriction or “no-go shoulder” of reduced cross-section in the well bore in the form of a landing or locating nipple. Typically the no-go shoulder provides a surface that restricts further downward passage of the tool. Force can then be applied to the tool to actuate the latch dogs and set the tool at a predetermined location along the length of the well bore. Alternatively, downhole tools and measuring devices are run into the bore of a well and landed in a so-called “side pocket mandrel” which has been installed as part of the drillpipe or tubing string when the well was cased. A side pocket mandrel typically has a main bore aligned with the bore of the drillpipe and a receptacle bore laterally offset from the main bore and extending alongside thereof. The receptacle bore typically has an electrical contact or prong in one end which is electrically connected to suitable equipment at the surface. Side pocket mandrels can be used for locating measuring devices used to monitor parameters such as downhole pressure and temperature whilst allowing other downhole tools to be lowered into the well. Side pocket mandrels are 99% used for gas injection or chemical injection. A retrievable valve is located in the side pocket which controls the flow of chemical or gas from the annulus to the production tubing.
Examples of downhole tools which are actuated by interaction with a restriction in a cased well bore are described in U.S. Pat. No. 4,823,872 (Hopmann) and AU703766 (McLeod). Examples of running tools which are used to position a tool in a side pocket mandrel are described in GB 2170247 (Schnatzmeyer) and U.S. Pat. No. 2,962,097 (Dollison).
Typically a running tool is used to land and set other downhole tools in a well. Once set, the downhole tool may be left in place for several hours or several days, while the running tool is retrieved to the surface. In recent times, running tools and downhole tools have been designed to be lowered, manipulated and retrieved using a conventional single or multi-strand electric cable known as ‘wire line’ or a single strand non-electric cable known as ‘slickline’.
Using traditional tools, it only possible to set the tools at the pre-determined locations where a landing nipple or side pocket mandrel has been pre-installed. The locations of the side pocket mandrels and landing nipples are fixed at the time when the well is designed and installed and add to the cost of designing the well. Moreover, in order to provide a plurality of landing nipples, the internal diameter of the casing becomes progressively narrower, making it increasingly difficult to accommodate and manipulate downhole equipment. Any restriction in the diameter of, in particular, a lower section of a well bore makes operation of the well more difficult and may lead to a significant loss of potential production from the reservoir. This loss of production is due to a pressure drop created across each well bore restriction. The smaller the restriction the greater the drop in pressure and the greater the drop in production rate as a result.
One type of downhole tool that may be landed, set and retrieved in a well bore is a bridge plug. A bridge plug is a device that is set across the bore of a cased well to test the pressure integrity of, isolate, or seal a section of the well bore. Bridge plugs may also be used to straddle a section of a cased well that has been perforated to flow test a formation. The bridge plug may be set as a permanent measure or be retrievable.
To perform the function of a bridge plug, the downhole tool must be able to be anchored in its set position in the well bore and form a seal to isolate a section of a cased well bore. Traditionally, bridge plugs are provided with an anchoring means on the plug itself arranged to engage at any depth within a given tubing internal diameter. Conventional bridge plugs require considerable force to be used to set the plug and to provide the necessary seal between the plug and the internal diameter of the cased well bore. This force is traditionally provided using explosive charges.
An alternative to traditional bridge downhole tools is described in U.S. Pat. No. 5,366,010 (Zwart). Zwart describes a retrievable bridge plug and running tool which can be set using wireline or slickline. The bridge plug of Zwart is provided with upper and lower sets of toothed locking slips which are movable into a radially extended bore wall engaging position by application of a downward force to a central sleeve along which an upper and lower member are axially slidable. After setting of the upper and lower slips, the bridge downhole tool of Zwart is brought into sealing engagement with the bore wall by application of an upward force to the lower member to compress a sealing means located between the upper and lower slips.
The Zwart design has several problems. The complex arrangement of nested sleeves results in a concomitant reduction in the internal diameter of the downhole tool itself. This makes it difficult to accommodate the passage of other downhole equipment through the hollow bore of the Zwart bridge plug to a lower level. The reduced bore of the Zwart bridge plug also restricts production flow through the internal diameter of the set bridge plug. The setting and retrieval operations of the Zwart bridge plug are quite complex, the Zwart bridge plug being provided with a large number of shear pins each of which control relative axial movement of a series of nested sleeves, the setting and retrieval operations requiring a complex series of upward and downward forces to be applied in a particular sequence to shear the pins in a particular order. Given that bridge plugs can be deployed at large depths down a well bore, it can be extremely difficult for a operator at the surface to determine whether or not the setting or retrieval operation is progressing as required when using the Zwart bridge plug. The present invention was developed to provide an alternative settable retrievable downhole tool that can be located at any depth within a well bore without needing an interaction between the well tool and a restriction or recesses within the well bore to land, set or retrieve the downhole tool.
It will be clearly understood that, although prior art use and publications are referred to herein, this reference does not constitute an admission that any of these form a part of the common general knowledge in the art in Australia or in any other country.
In the statement of invention and description of the invention which follow, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.